Using guitar amps?

I'm quiet new into bass playing. I've played guitar for four years but recently found out that I like the bass much more. One of my favorites is Bruce Foxton of the Jam (allthough I really like lots of differents sorts of music). For as far as I have found out he uses just ordanairy Marshall 100 watt guitar amps, with 4*4*12" speakers (or less depending on the gig.
Since I still have my guitar amp I tried it too and it doesn't sound to bad.
What I like to know is what are your opinions on it, are there risks? Is alapping to much for the speakers? What about the sound, and so on...
My amp is a Music Man 130 watt (so pretty loud) with 2*10". It's tube driffen so it has a nice drive sound at 6 or 7. I was thinking about adding a 1*15" speaker to it to get a little deeper sound and the suggestion of more volume.
I don't think it sounds as deep as most real bass amps, but that's sort of okay for the melodic pumping basslines I try to play. It has a deep switch wich helps a lot.
My bass is a Yamaha RBX 1000, an active bass with P and J style pick ups.
I'm hoping for some respons and answers, thanks in advance,

Hey Yvette, I'm a Bruce Foxton fan as well! Good to see someone else who recognizes him as a damn good bass player. Using a big amp like you're Music Man is usually fine for a straight ahead rock or punk...especially if you're going for that oldschool sound. Lemmy from Motorhead still uses Marshall guitar heads with 4X12 cabs. A lot of those Brit guys from that era used regular guitar stacks for bass....like Marshalls, Hiwatts, and Sound City amps. Back then you didn't have a ton of amp choices like you do now, especially with dedicated bass amps. Like you say...you don't get the same lows but for what you're into if it works that's all that matters. Sounds like your amp is perfect for that...and adding a 15" would probably help...just make sure you match the speaker impedence for your amp...otherwise you could really damage it, especially if its a tube amp. Who else are you into other than Foxton?

the reason why is this : a bassguitar's output is WAY higher than a guitar's output. So the input signal in the amp would be way bigger than the signal it was designed for.. so there's a chance you might blow up your amp..

Also.. a bass has lower sound ( hence the name " bass " ), and most guitar-speakers are unable to handle that sound properly.. so the sound would be crippled as well.. and ofcouse it goes without saying, that a serious bass-player wants nice low tones

Another risk with the speakers is.. if you turn it up too much the speaker will die..coz of the low-frequency..

If you ask me. i'd say : kick the guitar amp out and get a nice big bassamp

I thought the higher input could only damage the spekers. They don't sound like they are going to blow anyway, they just sound straught and solid not crippled at all.
I will never sell the amp (aswell as I will never sell my Strat, because I still like to play some guitar every now and then, just not in a band), but in the long run I think I will by a bass amp, till then I wanted to to use the Music Man, since it sounded way better then I expected. I thought adding the 15" would give me a start so later on I can buy a bass amp, and again later add an 4*10". I have thought about indepence, I can switch the amp to 4 ohm so if I add another 8 ohm cab I think it must be okay.

I don't know to many names of bass players but other bands I like are things like:

I have a very close friend who has been re-building a repairing tube amps for 25 years. He has a book that has wiring schematics for nearly every amp ever built.

He says (and backed it up with said book) that the differences between tube bass amps and tube guitar amps are minimal. A quick change of a capacitor here and there can change the voicing completely.

As mentioned, bass players have been using marshall heads forever. Many guitar players love playing through a Fender Bassman. All of those early Ampeg amps (pre SVT) were just amps. I see guitarists and bassists playing through them all the time. Same for acoustic, taynor and much of that vintage stuff.

You won't hurt anything playing through a guitar rig. If you are getting the sound you want you are fine.

My only concern is this: You typically will really crank a 130 watt amp to make a bass loud wereas a a guitar is so high-mid heavy that it is naturally loud. In order to get the tone/volume you want, you may be really pushing that head. Don't fry it.

There is some concern about pumping a ton of lows into the speakers. I wouldn't suggest pumping up the EQ to try to get more bottom out of it. You are using a guitar rig.

If you want/need more bass, try this at your next gig:

Get a DI box. A regular old rapco passive one will work, but an active one is probably better. It needs parrallel sends. Plug the bass into the DI. Send one to your amp. Mic the amp for "the tone" that you are are digging. Send the second signal straight to the board. You can then Dial up some bottom end on the DI signal using the board's EQ. Blend in the warm fuzzies of the miced tube amp for the meat of the tone. IF you have two channels on the board to spare for bass, you'll love the sound you get.

JetGlo took the words right out of my mouth - there weren't a lot of bass amp options then.

The early Marshall design is a little deceptive if the owner thinks they have an amp designed specifically for guitar.

Jim started out making bass cabs and PA gear. When he launched into mass production, he didn't set up a dedicated bass model and one for guitar. It was sort of a "one size fits all" and could handle both, at least in those days, (haven't played the 90's stuff).

Also, the whole Marshall/Vox/Orange retro-Britrock thing is part of the Jam image as opposed to being the best bass amp Foxton could find. I'd be a little wary of today's 18V basses through a vintage, unrestored Marshall.